1. Field of the Invention
The present invention relates to a terminal device, a method for acquiring drawing target, and computer-readable recording medium containing a computer program.
2. Description of the Related Art
In the past, a technique of converting an image obtained by a user drawing a desired character on a sheet or the like into digital data, combining the digital data with another image data, and displaying combined data has been known. Japanese Laid-open Patent Publication No. 2009-131596 discloses a system in which it is possible to enjoy a race in a pseudo manner using characters drawn by respective users.
For example, a scanner device scans an original obtained by the user drawing a character, and a computer connected to the scanner device extracts a character region from original image data obtained by scanning the original. The computer applies the image data in which the character region is extracted to a coordinate space by a computer.
For example, the computer binarizes original image data through threshold determination based on brightness values of pixels, and determines a drawing region and a non-drawing region on the binarized original image data in units of pixels. Then, the computer uses the region determined to be the drawing region as the character region.
Meanwhile, in the recent years, with the spread of multi-function mobile terminals such as smartphones or tablet-type computers, the performance of a digital camera mounted in the multi-function mobile terminal has been improved as well. If original image data is acquired by capturing an image of an original obtained by the user drawing a character through the digital camera mounted in the multi-function mobile terminal, the process of extracting the character region from the original image can be implemented without using the scanner device.
Meanwhile, original image data obtained by capturing an original image through a digital camera may be low in overall brightness or may have non-uniform brightness within an original plane due to a shadow or the like. In this case, it may be difficult to extract the drawing region properly although the binarization process is performed on the captured original image data.
In order to solve low brightness or non-uniform brightness in a captured image of an original image, a method of turning on a light installed in the multi-function mobile terminal is considered. When the light is turned on, influence of ambient light is reduced, and the occurrence of a shadow is suppressed. Further, as the light is turned on, low brightness can be expected to be solved. However, since the light mounted in the multi-function mobile terminal is commonly a point light source, an image captured in a state in which the light is turned on is bright in front of the light, that is, near a center of an original but dark in a peripheral portion, and thus an image is likely to have non-uniform brightness. In this case, there is a problem in that it may be difficult to properly extract the drawing region from the captured image data.
In view of the above-mentioned conventional problems, there is a need to make it possible to easily extract a drawing region from a captured image obtained by capturing an original.